March 23, 2013: Rihanna really BLACKED OUT on somebody yesterday . . . all because the girl said something RECKLESS on Twitter about an afterparty.

The backstory is that he girl attended Rihanna's CONCERT last night in Chicago. And then she attended an afterparty, which was ADVERTISED at the "OFFICIAL" afterparty. The flyers for the event said that Rihanna would attend.

Rihanna did not attend and the girl was mad so she put an angry - yet RESPECTFUL - message on Rihanna's instagram.